1. Technical Field
The present specification describes a head array unit and an image forming apparatus, and more particularly, a head array unit and an image forming apparatus including the head array unit for discharging liquid stably.
2. Discussion of the Background
An image forming apparatus, such as a copier, a printer, a facsimile machine, a plotter, or a multifunction printer having at least one of copying, printing, scanning, and facsimile functions, typically forms an image on a recording medium (e.g., a sheet) by a liquid discharging method. Thus, for example, a liquid discharging head discharges liquid (e.g., an ink drop) onto a conveyed sheet, and the liquid is then adhered to the sheet to form an image on the sheet.
Currently, there is market demand for an image forming apparatus capable of forming images at high speed. To accommodate such demand, the image forming apparatus may include more liquid discharging heads or nozzles or may increase a liquid discharging frequency. For example, a plurality of short liquid discharging heads may be combined into a long head array unit, so that the head array unit need not move in a main scanning direction to discharge an ink drop onto a sheet conveyed in a sub-scanning direction.
However, when the image forming apparatus includes many nozzles or drives the liquid discharging head at a higher frequency, a temperature of the liquid discharging head increases and thereby a temperature of ink contained in the liquid discharging head also increases, resulting in a change in ink viscosity. Consequently, the changed ink viscosity affects liquid discharging property of the liquid discharging head.
To address this problem, one example of a related art image forming apparatus controls an ink discharging signal based on the temperature of the liquid discharging head. However, when the liquid discharging head including many nozzles is driven at a higher frequency, the temperature of the liquid discharging head increases sharply, and thereby the image forming apparatus cannot adequately control the temperature of the liquid discharging head by controlling only the ink discharging signal.
To address this problem, another example of a related art image forming apparatus includes a head array unit in which a liquid channel is provided inside a head supporter for holding a base of the liquid discharging head. The liquid channel is provided separately from a shared liquid chamber containing ink to be discharged. Coolant flows in the liquid channel to maintain the temperature of the liquid discharging head at a constant level. However, coolant flows in the liquid channel provided in both ends of the base of the liquid discharging head only, and therefore does not cool a center of the base of the liquid discharging head, which easily stores heat, effectively.
Obviously, such insufficient cooling of the liquid discharging head is undesirable, and accordingly, there is a need for a technology to effectively suppress temperature increase of the liquid discharging head to maintain stable liquid discharging performance.